A transmission device, which performs radio communication of voice information and data of a mobile phone and the like, performs power amplification on a transmission signal to be output. To determine whether or not a prescribed output is output with respect to the transmission signal, the transmission device includes a detecting unit to monitor the output. If the transmission device does not obtain a desired output, the transmission device controls an output power according to a detection result.
For example, Japanese Laid-open Patent Publication No. 2003-8365 discloses a method for monitoring and controlling the power amplification. Japanese Laid-open Patent Publication No. 2003-8365 discloses that a direction coupler receives a signal according to the output signal output to an antenna side from one terminal, receives a reflection wave from the antenna side, and outputs the signal according to the reflection wave and that a detector detects the signal output. The control circuit described in Japanese Laid-open Patent Publication No. 2003-8365 may control the output voltage of a DC/DC converter based on a detection result.
For example, Japanese Laid-open Patent Publication No. 2001-16116 discloses a method for controlling the amplification of a transmission output by the power amplifier. Japanese Laid-open Patent Publication No. 2001-16116 discloses a first detecting unit that detects the transmission signal with a first detection sensitivity and discloses a second detecting unit that detects the transmission signal with a second detection sensitivity that is lower than the first detection sensitivity. Japanese Laid-open Patent Publication No. 2001-16116 controls the dynamic range of the amplifier by comparing the synthesized signal resulted in synthesis of the detected output signal to a transmission lamp generating signal.
As a high-speed communication standard of radio communication, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA) desire the transmission signal of which a large Peak-to-Average Power Ratio (PAPR) with respect to voice communication or constant speed packet communication (3GPP R99). That is, in the above-described communication standard, the transmission device is desired to handle a signal of which the rate of a peak power with respect to an average power is high. Regarding Long Term Evolution (LTE) or the like that is to be put to practical use in the future, for example, the modulation bandwidth of the transmission signal apparently varies up to 100 times at the maximum, so that the wider the bandwidth, the more the PAPR is increased.
Regarding the signal of which the PAPR is increased, if the electronic character of the transmission circuit is constant, the performance of Adjacent Channel Leakage power Ratio (ACLR) or Spectrum Emission Mask (SEM) specified in 3GPP is deteriorated compared to a case of handling the signal of the conventional constant speed packet communication standard (for example, R99). Therefore, comparing to the case of handling the conventional R99 communication signal, when using the signal such as the HSDPA, the HSUPA, and the LTE, the mobile communication terminal is desired to have a high saturation characteristic in the transmission circuit to achieve the appropriate performance according to the signal. In particular, a Power AMP (PA) of the transmission circuit of which the drive voltage is increased to raise the saturation point is provided to a market to correspond to the signal characteristic to be used.
Actually, however, if the PA drive voltage is increased, a communication time of a mobile communication terminal is shortened when current consumption is increased. Therefore, for example, the voltage is varied according to the type of the signal that is currently being transmitted or the control is performed to reduce the voltage when the transmission power is low.
The control is performed to change the PA drive voltage in such a way that the ACLR character is not deteriorated when the PA drive voltage is reduced and the transmission power is low or the PAPR of the transmission signal is different and the transmission signal type is different. The above-described control is performed by depending on the output power level that is set in advance and the transmission signal type such as the HSDPA, the HSUPA, the LTE, and the like.
The PAPRs are different from each other depending on a signal condition even if the signal types are similar. Regarding the voltage control of the PA according to the conventional transmission signal, for example, the drive voltage of the PA is set according to the theoretical maximum PAPR to correspond to all the PAPRs. As a result, there are many cases in which the voltage is increased more than necessary for the operation with respect to the PAPR of the signal that is actually being transmitted. Thus, there is a problem that the communication time is shortened as the power consumption is increased. The ACLR, the SEM, and the like specified by 3GPP are strongly correlated with the PAPR of the transmission signal. Therefore, for example, there is a method for controlling the drive voltage of the PA according to the signal PAPR that is being transmitted, so that the drive voltage is optimum most of the time if not always and a method of envelope tracking by varying the drive voltage of the PA according to a state of the transmission signal. However, when a large calculation circuit is desired, followability with respect to the modulated signal in a broadband such as the LTE is desired to be improved.
In general, the transmission circuit includes a nonlinearity of the PA in an area where the transmission power is high and includes a control function for correcting an output power error caused by a gain change due to a temperature variation or the like. For example, part of the output of the PA is extracted by a coupler, and the effective value of the output power is detected by a diode detector. The power that is actually being transmitted is measured based on the detected result, so that an error between the power and the target transmission power is corrected.
Japanese Laid-open Patent Publication No. 2003-8365 and Japanese Laid-open Patent Publication No. 2001-16116 do not have the disclosure or the suggestion of the above-described requirement and problem.